Double declutching

[Chris71]

Hi,

Can someone explain exactly how you should double declutch on a down change. As I udnerstand it, you

• clutch down
• into nuetral and clutch back up, so you've properly 'engaged' neutral
• raise the revs to spin up the layshaft
• clutch down
• back into (lower) gear and clutch up again

Having not tried it for a while, I seem to be having great difficulty doing this, but if raise the revs a second time, whilst the clutch is pressed down as you're going back into gear (ie during the penultimate step on the list above) it seems to work well. Produces a characteristic double blip of the throttle as you go down.

Am I really double declutching that way, or is it just leaving it to the syncromesh?

[gdaybruce]

Its all about timing, so that the gear cogs are spinning at matching speeds as you select the next gear. If you pause too long between the neutral / throttle blip and selecting the next gear, then you might as well not have bothered. You are looking to select the next gear while the cogs are spinning at the similar speeds and then to let the clutch up so that there is no jerk as the drive is re-engaged.

Practice makes perfect (especially if you have an old car with no, or knackered, syncromesh!).

[R_U_LOCAL]

Have a read here...

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[tuffer]

I tried this and nearly went through the windscreen, mental note to self "you drive an auto, you drive an auto, you drive......."

[Slowly Slowly]

Try this, drive along in forth gear at about 40 mph, check your revs (example 3000rpm) then drive along in third gear at 40 mph, check your revs (4200 rpm), the objective now is to drive along at 40mph in forth, dip you clutch, release clutch, blip throttle to take revs to 4200rpm(4300 rpm for good measure) dip your clutch, put it in 3 rd gear.
This way you brought the revs up to match the road speed in 3rd gear, don't over rev it, under rev it or take too long about it and it can't fail.
With experience all this has to be done by ear not by sight, you can't keep looking down at the rev counter/speedo.
When I've perfected heel and toe I'll let you know.

Edited by Slowly Slowly on Thursday 12th July 16:54

[RobM77]

Heel and toe with a single declutch is enough for most modern cars to be honest. For example, that was what I did in my last race car and I raced it for five years without being able to measure any wear at all on the clutch or gears over the whole period. Don't listen to people who tell you H&T isn't necessary on the road - the fact is that it makes driving much smoother and safer and is far kinder to the car.

A useful tip is to blip slightly higher than you need and engage as the revs are falling.

[Slowly Slowly]

My BMW2002 was perfect for H+T but my son has the car now, I have a TR7 V8 and the peddles are hopeless (bad workman blaming his tools) I end up braking then doing a quick tap dance on the peddles if I was giving myself marks out of ten I'd get about 3.

Which cars do you think are the best for it and is it possible to change my peddles to get the job done better?.

[RobM77]

Slowly Slowly said:

My BMW2002 was perfect for H+T but my son has the car now, I have a TR7 V8 and the peddles are hopeless (bad workman blaming his tools) I end up braking then doing a quick tap dance on the peddles if I was giving myself marks out of ten I'd get about 3.

Which cars do you think are the best for it and is it possible to change my peddles to get the job done better?.

The best cars for H&T to this day are still BMWs in my honest opinion. It's a combination of the floor hinged accelerator and the positioning. I've driven countless BMWs and all have been perfect for it. The only thing that's got in the way is drive by wire throttle that takes half a second to respond (affects all post 2000 model cars), which renders all modern petrol engined BMWs to the scrap heap - nice on Munich!

Caterhams are fully adjustable, which is nice; though strangely I've never managed to get mine as good to H&T in as a BMW!

The worst I've known, surprisingly, is the Lotus Elise. The worst of the breed were the early 111Rs with their dissapearing servo assisted brake pedal. There are aftermarket fixes available though if you know who to speak to.

Most cars can either be modified subtley (i.e. pedal height adjustment, extensions etc), or even have an entirely new pedal box put in.

[Slowly Slowly]

Look at the state them, you could drive with divers boots on and not catch the clutch when braking.

[GreenV8S]

Why are you double declutching at all?

[Chris71]

Why not?

I drive old (pre-synchromesh) cars every so often and also, I'm told the IAM favour doing so.

Slightly off topic, but I've tried heel and toe'ing numerous times and never got it even vaguely right! On the very rare occasions I've managed to contort my foot to get pressure on both pedals, I found it very difficult to judge the ammount of pressure I was applying to the brake!! Think I need pedal extensions....

[RobM77]

Chris71 said:

Why not?

I drive old (pre-synchromesh) cars every so often and also, I'm told the IAM favour doing so.

Slightly off topic, but I've tried heel and toe'ing numerous times and never got it even vaguely right! On the very rare occasions I've managed to contort my foot to get pressure on both pedals, I found it very difficult to judge the ammount of pressure I was applying to the brake!! Think I need pedal extensions....

In the right car it should just be a natural movement. On track I find that my threshold braking ability is reduced a bit by doing H&T, but for road use I don't find that H&T affects my braking at all. Not H&Ting would of course!!!!

[GreenV8S]

Chris71 said:

Why not?

Because it takes time and effort that can be better spent on other things? If your gearbox doesn't have working synchros then you may need to apply this sort of technique. However, if you have a modern gearbox in good condition it's completely unnecessary and simply wastes time and effort.

[sleep envy]

is it anything like cadence clutching?

[RobM77]

GreenV8S said:

Chris71 said:

Why not?

Because it takes time and effort that can be better spent on other things? If your gearbox doesn't have working synchros then you may need to apply this sort of technique. However, if you have a modern gearbox in good condition it's completely unnecessary and simply wastes time and effort.

Naturally, whilst double declutching might not be necessary, standard single declutch H&T is certainly a good idea for reasons of mechnical sympathy, passenger comfort and safety.

[Slowly Slowly]

RobM77 said:

GreenV8S said:

Chris71 said:

Why not?

Because it takes time and effort that can be better spent on other things? If your gearbox doesn't have working synchros then you may need to apply this sort of technique. However, if you have a modern gearbox in good condition it's completely unnecessary and simply wastes time and effort.

Naturally, whilst double declutching might not be necessary, standard single declutch H&T is certainly a good idea for reasons of mechnical sympathy, passenger comfort and safety.

First point,
I'm glad you mentioned "single declutch H+T" because this came as a great shock to me, professional driver for 35 years and didn't realise that some people do H+T with a single declutch, I still find it hard to understand, surely you have to get your foot off the clutch before you blip it or you are wearing the clutch out unnecessarily, having said that even this guy does it.

http://www.youtube.com/watch?v=rIivgrDsoUU&mod...


This guys H+T double declutch does look better and this is how I thought all H+T declutches where done

http://www.youtube.com/watch?v=WD5zq0Jkpoo


Second point.
If you are driving either a FWD or a RWD car you would get some engine braking by changing from top gear at 4800rpm to the next gear down unless you matched the engine revs with the road speed ie 5600 rpm in forth gear.
If you where in a high reving FWD car going round a slight curve in the wet just changing down without upping the revs before you release the clutch in forth gear will be like applying a front brake (admittedly only slightly but maybe enough to turn you around).
Even though you have a syncro box surely it's a safer way of driving?.

[GreenV8S]

Slowly Slowly said:

First point,
I'm glad you mentioned "single declutch H+T" because this came as a great shock to me, professional driver for 35 years and didn't realise that some people do H+T with a single declutch, I still find it hard to understand, surely you have to get your foot off the clutch before you blip it or you are wearing the clutch out unnecessarily,

Don't understand why you think that. The benefit of H&T is it lets you match the engine revs during a down-shift at the same time as braking. Whether you single or double declutch during the gearchange is a separate decision - you can use either technique separately, or both together.

Slowly Slowly said:

Second point.
If you are driving either a FWD or a RWD car you would get some engine braking by changing from top gear at 4800rpm to the next gear down unless you matched the engine revs with the road speed ie 5600 rpm in forth gear.
If you where in a high reving FWD car going round a slight curve in the wet just changing down without upping the revs before you release the clutch in forth gear will be like applying a front brake (admittedly only slightly but maybe enough to turn you around).
Even though you have a syncro box surely it's a safer way of driving?.

This is the whole point of matching engine revs during a gear change. It's particularly important in a powerful rwd car.

[RobM77]

I think you'll find that 99% of H&T drivers in modern cars use a single declutch. It won't wear the clutch out as the plates are apart during the blip. It might wear the release bearing out I suppose. The most important point is that you don't put that jerk through the driven wheels.

I've often gone against the grain and received criticism on this forum by suggesting that it is important to always be as far away from the limit of adhesion as possible when driving on the road. Most advanced drivers on here seem to advocate doing what you want so long as you don't breach the limit of adhesion. My point is that being as far away from the limit as possible means that if something untoward happens (mud on road, child jumps out etc etc), you've got less chance of losing control - plus of course you wear the car out less. For me, being further away from the limit means balancing the car properly, driving with smooth inputs and using H&T to do downchanges.

[Slowly Slowly]

GreenV8S said:

Why are you double declutching at all?

Have we got our wires crossed, Are you saying that instead of double declutching people should should only do a single declutch or.
Do a double declutch when not braking and a single declutch when doing H+T, you can't mean blip the throttle with your foot on the clutch, please don't tell me you mean that.


The phrase "you can't teach an old dog new tricks" springs to mind.

[RobM77]

Slowly Slowly said:

you can't mean blip the throttle with your foot on the clutch, please don't tell me you mean that.

Virtually everyone that uses heel and toe uses a single declutch per gear change and blips whilst the clutch is down (every single racing driver in the world does this!!). It's only vintage and some classic cars that require double declutching.